1. Field of the Invention
The present invention relates to a method for producing a liposome and an apparatus for producing a liposome. Specifically, the present invention relates to a method for producing a liposome which can be suitably used for pharmaceutical applications, and an apparatus for producing such a liposome.
2. Description of the Related Art
A liposome (hereinafter, also referred to as lipid vesicle) is a closed vesicle formed of a lipid bilayer membrane using lipids, and has an aqueous solution (outer water phase) in which liposomes are dispersed and a water phase (inner water phase) within the space of the closed vesicle. Liposomes have been studied for a variety of applications such as immune sensors, artificial red blood cells, and carriers of drug delivery systems taking advantage of the features such as barrier capacity, compound retention capacity, biocompatibility, the degree of freedom of setting the particle size, ready biodegradability, and surface-modifying properties. As for the application of a carrier, liposomes can encapsulate water-soluble compounds, lipophilic low-molecular weight and high-molecular weight materials, and a wide range of materials. In particular, in the case where the liposome is used as a carrier for a drug delivery system, the particle size of the liposome is preferably small from the viewpoint of permeability in biological membranes.
Liposomes can be prepared by stirring and emulsifying a water phase and an oil phase in a stirring apparatus. Since foaming may occur during the emulsification in a stirring apparatus, it is preferable to have a defoaming means.
With regard to the defoaming means, for example, JP2008-302264A discloses a defoaming tank including a tank body for containing a liquid to be treated in a state in which a liquid surface is vertically variable and a plurality of defoaming nozzles for diffusing and ejecting a defoaming liquid from above the liquid to be treated, in which bubbles contained in the liquid to be treated are defoamed by spraying the defoaming liquid from the plurality of defoaming nozzles toward the liquid surface of the liquid to be treated. It is also described that this defoaming tank is used in connection with a floating concentration column 6, which is an example of a solids floating apparatus. JP2006-297360A discloses a liquid circulation type reduced pressure concentration apparatus consisting of a preheating reservoir tank for a foamable liquid, a defoaming machine and a condenser, which is configured to prevent foaming in such a way that a rotating body is placed in the defoaming machine, the foamable liquid preheated in the preheating reservoir tank is fed into the rotating body of the defoaming machine, and the liquid droplets are finely dispersed into fine particles and released from the rotating body. JP1995-328620A (JP-H07-328620A) discloses a centrifugal sedimentation type centrifuge apparatus for removing a solid from a mixture containing a liquid and a solid having a specific gravity smaller than that of the liquid, which is characterized by providing a rotor having an inside disc. It is also stated that a defoaming tank is provided. JP2000-027024A discloses an oil agent defoaming apparatus formed by connecting an oil agent tank and an oil agent application device to an oil agent delivery pipe and an oil agent return pipe, characterized in that a suction device having a suction port for sucking bubbles in the oil agent tank is provided such that the distance between the oil agent liquid surface in the oil agent tank and the suction port is 50 to 110 mm. JP2003-113596A discloses a defoaming apparatus having a function of sucking bubbles from a liquid surface and breaking the bubbles by a centrifugal force of a rotating body and then returning the swollen liquid back to the liquid surface.